I'm wondering if Heat Metal could force a target to drop their shield.
The spell description says (emphasis mine):
If a creature is holding or wearing the object and takes the damage from it, the creature must succeed on a Constitution saving throw or drop the object if it can.
Since doffing a shield is an action, they cannot drop their shield on the caster's turn when they take the damage and fail their save.
So if the target fails their save, are they then required to use their action on their turn to drop their shield, or are they free to hold onto their shield?